A liquid crystal display apparatus must have polarizing plates arranged on both sides of a glass substrate forming the surface of a liquid crystal panel due to its image forming system. An example of such a polarizing plate to be used is generally manufactured by attaching a polarizer protective film formed of a cellulose-based resin film such as triacetyl cellulose on each side of a polarizer made of a polyvinyl alcohol-based film and a dichromatic substance such as iodine by using a polyvinyl alcohol-based adhesive.
However, the cellulose-based resin film has insufficient heat and humidity resistance and thus has a problem in that properties such as a degree of polarization and a hue of a polarizing plate degrade when a polarizing plate using a cellulose-based resin film as a polarizer protective film is used under high temperature or high humidity conditions. Further, a cellulose-based resin film causes retardation with respect to incident light in an oblique direction. With recent increase in size of a liquid crystal display, increasingly, the retardation has significant effects on viewing angle properties.
As a resin material excellent in heat resistance and optical transparency, a (meth)acrylic resin such as polymethylmethacrylate is well known. However, the (meth)acrylic resin is brittle and is easily cracked, which causes a problem in transportation such as breakage during film transportation, and a problem of poor productivity. Therefore, it is difficult to use the (meth)acrylic resin as it is for a polarizer protective film.
In order to solve the above problems, a polarizer protective film is proposed, which is formed of a composition composed of an acrylic resin (A) containing methyl methacrylate as a main component and a toughness modifier (B) (preferably, shock resistant acrylic rubber-methyl methacrylate graft copolymer and a butyl-denatured acetyl cellulose) (see Patent Document 1). However, the polarizer protective film has a problem in that a relatively great amount of the toughness modifier (B) is used so as to enhance the mechanical strength (acrylic resin (A)/toughness modifier (B)=60/40 to 90/10 in a weight ratio), and consequently, the high heat resistance, high transparency, and high optical characteristics originally owned by the acrylic resin (A) may be impaired.
On the other hand, as a resin having higher heat resistance, higher transparency, and higher mechanical strength compared with a conventional (meth)acrylic resin such as methyl methacrylate, a (meth)acrylic resin having a lactone ring structure is known (see Patent Document 2). However, in the case of using the (meth)acrylic resin having a lactone ring structure as a polarizer protective film as it is, when an easy adhesion treatment (for example, a corona treatment) is conducted with respect to a film surface so as to enhance the adhesion with respect to the polarizer, a cohesive failure may occur in the vicinity of the surface of the film, and the adhesion with respect to the polarizer may not be exhibited sufficiently.    Patent Document 1: JP 05-119217 A    Patent Document 2: JP 2001-151814 A